Yes, size attribute just ignored. Only "color" and "face" attributes are taken into account.
From Html class sources:
private void handleStartTag(String tag, Attributes attributes) {
    if (tag.equalsIgnoreCase("br")) {
        // We don't need to handle this. TagSoup will ensure that there's a </br> for each <br>
        // so we can safely emite the linebreaks when we handle the close tag.
    }
    ...
    else if (tag.equalsIgnoreCase("font")) {
        startFont(mSpannableStringBuilder, attributes);
    }
    ...
}
private static void startFont(SpannableStringBuilder text,
                              Attributes attributes) {
    String color = attributes.getValue("", "color");
    String face = attributes.getValue("", "face");
    int len = text.length();
    text.setSpan(new Font(color, face), len, len, Spannable.SPAN_MARK_MARK);
}